Method and apparatus for planning or controlling a radiation treatment

ABSTRACT

The present invention relates to method for generating planning data or control data for a radiation treatment, comprising the following steps: acquiring segmented data of an object which contains a treatment volume and a non-treatment volume; modelling at least some or all of the volume or surface of the treatment volume as a source of light or rays exhibiting a predefined or constant initial intensity; modelling the non- treatment volume as comprising volumetric elements or voxels which each exhibit an individually assigned feature or attenuation or transparency value (t min ≦t≦t max ) for the light or rays which feature is assigned to the light or ray or which attenuation or transparency maintains or reduces the intensity of the light or ray as it passes through the respective volumetric element or voxel, wherein the feature or attenuation or transparency value is individually assigned to each volumetric element or voxel of the non-treatment volume; defining a map surface which surrounds the treatment volume or the object; calculating an accumulated intensity value for points or areas on the map surface, the accumulated intensity being the sum of the intensities of all the rays which exhibit the predefined or constant initial intensity and are emitted from the volume or surface of the treatment volume and reach a respective point on the map surface preferably by following a straight line, wherein if the ray passes through a non-treatment volume or voxel, the intensity of the respective ray is reduced or attenuated by a factor which is determined by the individual feature or attenuation or transparency value of the respective non-treatment volume or voxel; and generating an intensity distribution on the map surface using the calculated accumulated intensities.

The present invention relates to a method and an apparatus for planningor controlling a radiation treatment, such as for example a tumourradiation treatment, wherein the tumour may be surrounded by or locatednext to healthy tissue or organs which are to be protected and/or onlyminimally affected by the radiation treatment.

In particular, this invention relates to radiation therapy planning andradiation therapy equipment for the treatment of tumours or the like andspecifically to a radiation therapy planning method for calculating ordetermining good or optimum points or areas on an object or a patient tobe treated for delivering radiation in order to achieve the desiredtreatment at a treatment area within the object or patient whileavoiding damage to tissue or organs to be protected or at least reducingor minimising the impact of said radiation on areas or volumes to beprotected.

Radiation therapy refers to the treatment of a specific tissue, forexample a tumourous tissue, using externally or internally appliedhigh-energy radiation. The direction and placement of the radiation mustbe accurately controlled in order to ensure both that the treatmentvolume or tumour receives a desired or sufficient amount of radiation inorder to be treated or destroyed and that damage or negative effects tothe surrounding healthy or non-tumourous tissue is/are avoided orminimised.

An external-source radiation therapy, as preferably used in the presentinvention, uses a radiation source which is external to thepatient—typically either a radioisotope or a high-energy x-ray sourcesuch as a linear accelerator. The external source produces a collimatedbeam which is directed onto and into the patient in order to reach thetreatment volume or tumour site. In most cases, however, anexternal-source radiation therapy also undesirably but necessarilyirradiates a volume of non-tumourous or healthy tissue lying in the pathof the radiation beam along with the tumourous tissue or treatmentvolume.

The adverse effect of irradiating healthy tissue can be reduced, whilestill maintaining a given dose of radiation in the tumourous tissue ortreatment volume, by projecting the external radiation beam into thepatient at a variety of gantry angles with the beams converging on thetumour site. It is then desirable to obtain information concerning oneor more preferred directions and/or entry points of the radiation beamwith respect to a patient or body, so that a significant amount of theenergy delivered by the radiation beam from these directions and/or atthese entry points is delivered to the treatment volume or tumouroustissue, while healthy tissue or organs located next to the treatmentvolume and/or at least partly surrounding the treatment volume are notor only minimally affected by the radiation beam.

U.S. Pat. No. 5,418,827 discloses a method for radiation therapyplanning, wherein a distribution of electrical charges within aconductor is determined which would produce a potential energy fieldwhich matches the desired dose to the tumour in the plane of theradiation therapy machine. The fluence of any given ray through thetumour is determined by summing the charges along the ray's path.

It is an object of the present invention to provide a method and anapparatus for improving the planning or controlling of a radiationtherapy treatment.

This object is solved by the subject-matter of the independent claims.Advantageous aspects of the invention are disclosed in the following andcontained in the subject-matter of the dependent claims. Differentadvantageous features can be combined in accordance with the inventionwherever this is technically expedient and feasible.

In accordance with a method for generating data or information forplanning a radiation treatment or for controlling a radiation treatment,for example by controlling the operation of a radiation device which isknown in its own right, data of the body or object to be treated areacquired. The data are preferably 3D data or volumetric data which canbe obtained by known imaging methods which generate image data ofanatomical structures, such as the soft tissue, bones, organs, etc. of abody. A medical imaging method can be an apparatus-based imaging method,such as for instance computed tomography (CT), cone beam computedtomography (CBCT, in particular volumetric CBCT), x-ray tomography,magnetic resonance tomography (MRT or MRI), sonography, ultrasoundexamination, positron emission tomography or any other imaging methodwhich generates a three-dimensional data set as an output which is arepresentation of the imaged object or body.

The data used by the method according to the invention are eitheralready segmented or are to be segmented for example using known methodssuch as atlas segmentation. An atlas typically consists of a pluralityof generic models of objects, wherein the generic models of the objectstogether form a complex structure. When segmenting medical images, theatlas is matched to medical image data and the image data are comparedwith the matched atlas in order to assign a point (such as a pixel orvoxel) of the image data to an object of the matched atlas, therebysegmenting the image data into objects such as for example bones,organs, blood vessels, nerves and so on.

Some anatomical structures are unlikely to be fully and/or easilydetectable using atlas segmentation. In particular, pathological changesin tissue structures, such as tumours, may not be easily detectable andmay not be visible in images generated by the imaging methods mentioned.However, these structures—such as primary/high-grade brain tumours—canbe made visible in MRI scans by using contrast agents to infiltrate thetumour. In the case of MRI scans of brain tumours, the signalenhancement in the MRI images due to contrast agents infiltrating thetumour can be considered to represent the solid tumour. Thus, a tumourcan be detected and can in particular be discerned in the imagegenerated by the imaging method.

Any way of providing segmented data can be used, including for example acombination of atlas segmentation and images taken while using contrastagents.

The area or volume to be treated, such as for example tumourous tissueor a tumour, is referred to in the following as a “treatment volume” andis formed as a treatment volume model within the above-mentioned imagedata. If a tumour is located in or adjacent to surrounding tissue, thewhole tumour or tumourous tissue is modelled as a treatment volumecomprising a treatment volume surface which separates the treatmentvolume from the surrounding and/or adjacent tissue or structures of theobject or body, which then represent a non-treatment volume.

In accordance with the invention, the treatment volume andadvantageously (e.g. to reduce the computing time) only the surface ofthe treatment volume is considered or modelled as a preferablycontinuous source of rays, such as light, or as an illuminant whichemits light or rays, all rays preferably having the same initialintensity value of for example 100, along one or more straight lines orpaths in the direction of the outside of the body within which thetreatment volume is located, i.e. simulated rays are projected from thetreatment volume or tumour to the outside. The treatment volume ortumour can be considered as a volumetric light source. Alternatively,the treatment volume or the treatment volume surface is modelled orconsidered to have a number of areas or point-shaped sources of light orrays or ray starting points which are distributed uniformly or randomlyacross the treatment volume surface or even within the treatment volume.The light or rays start or emerge from the treatment volume surface andspread out in every direction, preferably with the exception of thetreatment volume itself, i.e. light or rays emitted from the treatmentvolume surface preferably do not pass through the treatment volumeitself.

If some parts or areas of the treatment volume shall receive a higherdose of irradiation during later radiation treatment, such as e.g.malignant parts of a tumour, the initial intensity value of the raysemerging from the tumour or its surface can be increased (to be e.g.150) compared to rays emerging from non-malignant parts of the tumour.The rate of cell division of a tumour can be used to determine theinitial intensity value, so the initial intensity value can for examplebe a (linear) function of the rate of cell division.

It is to be noted that the terms “light”, “ray”, “opacity”,“transparency” and “intensity” as used here do not refer to actualoptical arrangements or processes but rather to simulation orcalculation methods.

The non-treatment volume which is adjacent to and/or surrounds at leasta part of the treatment volume is segmented as mentioned before, and thesegmented elements such as organs, blood vessels, nerves and so on areconsidered or modelled in accordance with the invention, in order tohave an assigned feature, such as to reduce the intensity of a transientray by a predetermined absolute factor or by a factor per unit length.The non-treatment volume can be considered to have an at least partiallytransparent volume or area which exhibits an individual transparency ortransparency distribution which can also be considered to have theopposite property, i.e. an opacity distribution. So-called organs atrisk (OARs) are for example modelled to have a relatively lowtransparency, in order to largely reduce the intensity of a transientray, or even to be opaque so as not to allow light or a ray to passthrough (i.e. the intensity of the exiting ray is 0). Organs or (tissue)structures which are less affected by radiation are for example modelledor considered to have a relatively high transparency (for example 0.8 to1), i.e. for example these organs or structures allow light or raysemitted from the treatment volume surface to pass through with noattenuation or intensity reduction (i.e. transparency=1) or with onlyrelatively little attenuation or intensity reduction. In order to modelstructures or organs as having a respective individual and probablyuniform (within the structure) and predefined feature, such as atransparency, a volume element (voxel) belonging to the respectivestructure or organ can be defined as having a specifically assignedpredefined feature, such as a transparency or opacity. A specific organor structure is for example formed or modelled by voxels which all havethe same transparency or opacity within the volume of the structure ororgan.

By using a continuous or almost continuous representation of the organcoverage information, the tumour extent is rendered in the image. Usingvolumetric rendering, the distance from the tumour and the outer contourcan also be included. This continuous map allows algorithms to easilyfind local and global minima for organ coverage.

Once the structures or organs of interest or the entire non-treatmentvolume which is adjacent to and/or surrounds at least a part of thetreatment volume is modelled to have a respective individual feature,such as a transparency or transparency distribution, which can forexample be accomplished by defining the transparency or opacity of therelevant voxels (for example only organs at risk) or of each voxel ofthe volume of the body except the treatment volume, the light or lightintensity or rays which reach the outside of a body to be treated arecalculated, or an area such as a sphere is calculated which surroundsthe treatment volume and preferably has its centre at the intendedisocentre located within the treatment volume. The isocentre can be thecentre of mass of the treatment volume. This area or sphere is referredto as a “map surface” or “collision map”.

In order to calculate the projection or intensity of the light or rayswhich are emitted from the treatment volume itself, for example thebarycentre, or the treatment volume surface, and reach the outsidesurface of the body or an area, such as a sphere, surrounding thetreatment volume or the body, the paths of several rays have to beconsidered. A calculation or simulation is performed in order toascertain which of the above-mentioned modelled non-treatment structuresexhibiting an individually assigned feature, such as atransparency/opacity, or voxels with an individually assigned feature,such as a transparency/opacity, are passed along a straight line of theray, wherein these structures or voxels all influence the light rays orattenuate the intensity of the light or rays emitted from the treatmentvolume surface, for example by a factor of between 0 and 1.Alternatively, the respective features(s) are assigned to the light orrays passing the non-treatment structures or voxels having theseindividually assigned feature(s). Using this approach, light or raysemitted from the tumour are shadowed by the surrounding OARs. Thissimplified problem is similar to a problem experienced in computergraphics, namely that of calculating the shadows of volumetric light.Each ray or light beam is ever increasingly attenuated as it passesthrough areas exhibiting a transparency other than 1, i.e. each ray orlight beam is affected by all the transparency or opacity values on itsway to reaching the outer surface. If, for example, a ray is emittedfrom the treatment volume surface which has a predefined simulatedinitial intensity of 100, and this ray passes along a first distance d₁which includes an organ at risk (see OAR1 in FIG. 1) exhibiting anassigned predefined transparency (of t₁/unit length), then this ray isattenuated by: d₁·t₁/unit length. The (virtual) intensity of this ray asit exits the respective structure is then given by:

I _(exit) =I _(center) d ₁ ·t ₁/unit length

This calculation can be repeated if more structures or organs exhibitinga predefined transparency of for example t<1 are also situated in thepath of the respective ray. The transparency t of a structure or voxelwhich is not or not appreciably affected by radiation can be set to 1.

Although possible, it is preferred if physical effects such asdeflection, reflection, diffusion or scattering of the rays or lightbeams are not considered. A calculation is preferably performed in orderto ascertain how rays or light beams which are emitted from thetreatment volume surface and exhibit for example an initial intensity of100 are attenuated by the respective transparent (t=1) orsemitransparent (0<t<1) or opaque (t=0) volumes or voxels which exhibitan individually assigned transparency or opacity (o=1-t) while followinga straight line on their way from the outer surface of the treatmentvolume to the surface onto which said rays are incident, such as asphere centred around the treatment volume or a barycentre of thetreatment volume, all or at least some of the surface of which ispreferably outside the body within which the treatment volume islocated. The outer surface or sphere which is considered as a mapsurface will then have an intensity distribution formed by the (probablyattenuated) intensities of all the rays which reach this outer surfaceor sphere. It is to be noted that more than one ray can reach a singlepoint of the outer surface or sphere, since the rays preferably do notstart at a single point but rather from some or all of the points of thetreatment volume, preferably in a distribution across the outer surfaceof the treatment volume.

When modelling the treatment volume or its surface as a source of light,this volume or surface can be modelled either as a homogenouslyilluminated or illuminating volume or surface or as a plurality oflight-emitting points which are preferably evenly distributed over thevolume or surface or distributed over the volume or surface using MonteCarlo techniques.

Once all the rays or light beams emitted from the entire volume orsurface of the treatment volume or from all the emitting pointsdistributed within the volume or over the treatment volume surface havebeen considered, and all the effects of at least partially transparentor opaque volumes or voxels along the straight path of the light orbeams from the treatment volume surface to the map surface have beencalculated, an intensity image or labelled image based on all these raysis calculated, wherein each point on the map surface is assigned anintensity or colour value depending on the amount of the intensities ofall the rays or light beams reaching this point. If, for example, anorgan to be protected from irradiation is on the path of all the beamsemitted from the treatment volume surface to a specific part of the mapsurface, then this part of the map surface will for example receive noray exhibiting an intensity greater than 0 and will thus for exampleappear black, whereas a map area will for example appear white if thereis no organ at risk between the treatment volume surface and thecorresponding map surface, i.e. a number of rays with an unattenuatedintensity of for example 100 reach this point and are then summed to forexample 100 (number of rays reaching said point). Depending on thesummed or integrated amount of transparent volumes or opaque voxels inthe path of all the light beams reaching the map surface, theintensities or colour values of the map surface points or pixels canhave any intermediate value between a minimum, for example 0%(indicating for example an improper point for irradiation), and amaximum value, for example 100% (indicating for example an optimum pointfor irradiation), in order to indicate what amount of non-transparent orsemi-transparent volumes (i.e. organs to be protected) are situated onthe path from the treatment volume surface to the respective map surfacearea or point.

The accumulated intensity of a map surface point can for example bedefined as

I_(map)=ΣI_(i);

wherein ΣI_(i) is the sum of the intensities of all the rays reachingthis map surface point.

If the respective non-treatment structures or volumes do not have afixed assigned value or feature, such as a predefined opacity, theaccumulated intensity I_(map) can be calculated to be a function ofvariables, such as variable opacities, so that e.g. the individual OARscan be given different weights or opacities after calculating the(variable) intensities of the map surface.

The highest value of the accumulated intensity of all the map surfacepoints can be defined as 100% (or as being “light”, see for exampleFIGS. 1 and 3).

It is to be noted that a single point on the map surface can be reachednot only by a single ray emitted from a single point on the treatmentvolume surface but also by additional rays and, depending on theinternal opacity or transparency of the body volume structure, possiblyeven by all the rays emitted from the treatment volume.

Alternatively, all rays emitted from the treatment volume surface on theside of the treatment volume surface on which the point of the mapsurface is located are considered. For example, in this case only therays emitted from the rear side of the treatment volume surface withrespect to a point on the map surface will not reach this map surfacepoint, since the treatment volume itself can in such an alternativeembodiment be considered to be fully opaque, i.e. does not allow any rayemitted from the treatment volume surface to pass through the treatmentvolume itself.

The colour or shadow or intensity image thus generated on the mapsurface can be interpreted as indicating the extent to which tissue isto be protected, which is then consequently modelled as exhibiting aspecific transparency or opacity (i.e. for example opaque if it is to befully protected, 20% to 80% transparency if it is expediently protected,and fully transparent if it need not be protected) which is theneffected when irradiating the treatment volume with a ray projected fromthe respective map surface point onto the treatment volume or its centre(i.e. the reverse direction of the above-mentioned simulation).

However, this scenario only covers the unrealistic prospect that theradiation stops within the treatment volume.

Since a treatment ray will have a certain (desired) effect within thetreatment volume, but will still emerge from the treatment volume, it isnecessary to consider not only the intensity value of a pixel or area onthe map surface but also the intensity value on the opposite side, forexample the point on the map or sphere surface which is the exit pointof the irradiation ray when radiation is delivered through the entrypoint on the map surface and passes through the treatment volume. If themap surface is modelled as a sphere, the exit point is the pointobtained when mirroring the entry point at the centre point of thesphere, which is preferably the centre of mass of the treatment volume.

In order to determine whether or not it is expedient to irradiate thetreatment volume with a ray emanating from or passing through a point onthe map surface, the accumulated intensities of all the incoming rays atboth the entry point and the (mirrored) exit point are preferablyconsidered. In its simplest form, the two accumulated intensities can beadded, such that one hemisphere of the map surface shows a distributionof accumulated intensities and the other hemisphere shows the intensitydistribution mirrored at the centre of the sphere.

If there is any tissue or organ or volume in the line of the radiationbeam which is to be protected or less affected, this volume to beprotected is preferably located behind the treatment volume (i.e. theradiation beam passes through the front non-treatment volume first, thenpasses—probably with a low attenuated irradiation intensity—through thetreatment volume, and then—with an even further reduced irradiationintensity—through the tissue or organ or volume to be protected), henceit is advantageous to not simply sum the accumulated intensities of thesimulated rays which reach an entry point and the corresponding exitpoint of a radiation beam, but rather to also take into account whetheror not volume to be protected is located in front of or behind thetreatment volume. For this purpose, the intensities at corresponding(mirrored) entry and exit points should only be the same if the sameamount of opaque volume or voxels is located between one (entry or exit)point and the treatment volume as is located between the other (exit orentry) point and the treatment volume. In all other cases, it isadvantageous for the accumulated intensity of a map surface point to behigher at the point which has less opaque volume (to be protected)between this point and the treatment volume, as compared to the amountof opaque volume located between the treatment volume and the opposing(mirrored) point which is then designated as the exit point. In order toachieve this result, the accumulated intensity at one point is comparedto the accumulated intensity at the opposite (mirrored) point, and ifthe first intensity is higher than the accumulated intensity at themirrored point, this indicates that irradiation should preferably bestarted from this point and not from the opposite point, since more ofthe volume or tissue to be protected will then be located behind and notin front of the treatment volume. This can be indicated or made visibleby for example adding a predefined amount of (simulated light) intensityto the added or integrated amount of intensity at the point on the mapsurface exhibiting a higher total value for the accumulated intensity orby subtracting a predefined amount of (light) intensity from theopposite map surface point, for example:

If I_(map,1) is the accumulated intensity at a map surface point andI_(map,2) is the accumulated intensity at the opposite or mirroredpoint, the following calculation for the resulting map surfaceintensities can be made:

I _(map,1,adjusted) =I _(map,1) +I _(map,2) +I _(adjustment) and

I _(map,2,adjusted) =I _(map,1) +I _(map,1),

if I_(map,1)>I_(map,2)

I _(map,1,adjusted) =I _(map,1) +I _(map,2) and

I _(map,2,adjusted) =I _(map,1) +I _(map,2)

if I_(map,1)=I_(map,2)

I _(map,1,adjusted) =I _(map,1) +I _(map,2) and

I _(map,2,adjusted) =I _(map,1) +I _(map,2) +I _(adjustment)

if I_(map,1)<I_(map,2).

I_(adjustment) can be any positive value, for example 100.

A surface map is thus generated which not only indicates preferredpoints for irradiating the treatment volume in order to protect organsat risk, but also only takes into account the position of the organs atrisk with respect to the treatment volume when preferably located behindand not in front of the treatment volume as viewed along the line of theradiation beam.

The transparency, lucency or opacity of a volume or voxel can bedetermined or can be predefined depending on one or more of thefollowing: distance from the surface, functional aspects, thesensitivity to radiation of the structure or organ concerned; thedistance from the treatment volume; and the importance of the structureor organ concerned. The transparency can for example be set to zero (orthe opacity set to a maximum value) for a structure or organ whichshould not receive any radiation at all, such that no simulated light orray exiting the treatment volume surface is allowed to pass through andblack areas are generated on the map surface which indicate that noradiation is to be directed onto the treatment volume from this point ofthe map area. Conversely, tissue or organs which are less affected byradiation are modelled as exhibiting a high degree of transparency (orlow opacity), thus generating a bright area on the map surface whichindicates that starting irradiation of the treatment volume from thispoint is less harmful to the body as a whole.

The invention also relates to a program which, when running on acomputer or when loaded onto a computer, causes the computer to performthe method as described above and/or to a program storage medium onwhich the program is stored (in particular in a non-transitory form)and/or to a computer on which the program is running or into the memoryof which the program is loaded and/or to a signal wave, in particular adigital signal wave, carrying information which represents the program,in particular the aforementioned program, which in particular comprisescode means which are adapted to perform all the steps of the method asdescribed above.

The invention also relates to a planning or control system for aradiation treatment device comprising: the computer as described above,for processing the three-dimensional or volumetric image data of a bodyand for calculating a quantitative value for the suitability of possibleradiation entry and exit points as set forth above; a data interface forreceiving the three-dimensional data and optionally for outputtingcontrol data to an irradiation device; and optionally a user interfacefor receiving data from the computer in order to provide information toa user, wherein the received data are generated by the computer on thebasis of the results of the processing performed by the computer inaccordance with the method described above.

In addition, a radiation treatment device is provided which iscontrolled with respect to the position of the radiation-emittingelement relative to the body or treatment volume, on the basis of theresults of the data outputted from the computer which quantitativelyindicate which relative positions or irradiation directions or pointsare preferred and/or less harmful as compared to other possibleirradiation points or directions.

Additional advantageous features are disclosed in the following detaileddescription of embodiments. Different features of different embodimentscan be combined.

FIG. 1 schematically shows an intensity profile being generated on a mapsurface in accordance with the invention;

FIG. 2 shows an intensity profile being generated on a map surface in asimple manner;

FIG. 3 shows an example embodiment based on the example of FIG. 1; and

FIG. 4 schematically shows a treatment system which can he controlledusing planning data or control data generated in accordance with theinvention.

FIG. 1 shows a schematic representation of a method for generatingplanning or control data, wherein a cross-sectional view of an objectcontaining a tumour as a treatment volume and containing a volumesurrounding the treatment volume as a non-treatment volume including twoorgans at risk (OAR) is shown. It is to be noted that the boundary ofthe object can also be the semi-circle shown which is the map surface onwhich the intensity profile is depicted and will usually be between thismap surface and the treatment volume, as shown in FIG. 1.

The treatment volume or tumour volume is determined, for example on thebasis of a three-dimensional MRI data set which is segmented using knownmethods so as to also obtain the boundaries of the organs at risk shown(OAR1 and OAR2) which are located within the same body. These organs atrisk OAR1 and OAR2 are to be protected from receiving a high dose ofradiation or possibly even from receiving any radiation at all in thecourse of a radiotherapy treatment,

In order to determine an expedient location on the circular map surfaceshown, from which an irradiation beam can be projected in a straightline towards the centre of mass of the treatment volume or tumour, thetreatment volume or tumour surface is considered to emit light or raysalong a straight line in all possible directions, with the exception ofdirections leading into the treatment volume itself. The organs at riskOAR1 and. OAR2 are considered or modelled to have a predefined opacityor transparency which for example does not allow any ray emitted fromthe treatment volume surface to pass through or which alternativelyreduces the intensity of a ray emitted from the treatment volumesurface, by a specific fixed factor of for example 50%, when passingthrough an organ at risk, or reduces it by a factor which is determinedon the basis of the distance by which a ray penetrates said organ atrisk when passing through it along a straight line. The organ at riskcan for example be assigned a transparency of 0.9 which would thenreduce the intensity of a ray by 10% per unit length, such that forexample a ray traversing this organ at risk along one unit length wouldbe reduced in intensity by 10%, a ray traversing the organ at risk alonga distance of two unit lengths would be reduced in intensity by 20%, andso on.

Depending on the vulnerability of the segmented volume or organ at riskto radiation, the transparency or opacity of the volume or pictureelements or volume elements (voxels) belonging to the respective organor non-treatment volume can be selected. If the organ is not to receiveany radiation at all, the opacity is set to 100%, i.e. the transparencyis set to 0%; in other words, no ray emitted from the treatment volumeis allowed to pass through, thus effectively reducing the intensity ofthis ray to 0%.

If a structure or tissue is not appreciably affected by radiation, thetransparency is set to 1 or 100%, i.e. a ray passes through itunattenuated, without its intensity being reduced.

A table showing an example set of values for non-treatment organs ortissues to be used is given below:

TABLE 1 Transparency Structure/organ (vulnerability) Tissue 100% or 1Bones  80% or 0.8 Nerve system  5% or 0.05 Blood vessel  20% or 0.2Liver tissue  0% or 0 Pulmonary tissue  0% or 0

It is to be noted that the above example is not binding or limiting andthat other intensity values for a volume or voxel belonging to aparticular structure can be chosen.

According to a separate, independent approach, the importance of therespective volume can be considered, wherein a voxel belonging to aparticular volume is assigned an intensity which is lower, the greaterthe importance of the respective structure. An example of assigningtransparency values is shown in Table 2 below.

TABLE 2 Transparency Structure/organ (importance) Tissue 100% or 1 Bones 90% or 0.9 Nerve system  0% or 0 Blood vessel  30% or 0.3 Liver tissue 20% or 0.2 Pulmonary tissue  10% or 0.1

The two approaches above, i.e. defining the transparency on the basis ofthe vulnerability of the volume to radiation and on the basis of theimportance of the volume, can be combined if desired. Thus, if bothfactors are considered, the respective transparency values assigned to arespective single voxel can be multiplied, in order to obtain a combinedtransparency value which can be used for the subsequent calculation andsimulation, according to the following formula:

T _(combined) (voxel)=T _(vulnerability) (voxel)*T _(importance)(voxel).

In accordance with another independent aspect, the transparency (oropacity) of a volumetric element can depend on the distance from thevoxel to the treatment volume. It can for example be defined such thatthe closer the voxel is to the treatment volume, the higher thetransparency of the respective voxel is set. The transparency T can forexample be calculated by:

T=1/d (patient surface)

wherein d (patient surface) is the minimal distance to the surface ofthe patient. This distance can for example be read from a predefineddistance map.

Regarding a ray exiting the treatment surface, the same approach can beused. More preferred, the length of a vector connecting the respectivepoint with the patient surface and running through the centre of thetreatment volume is chosen.

If, for example, a sphere is used as a map surface has a radius r whichis the distance from the map surface to the centre of mass of thetreatment volume, then the transparency of a respective voxel can bedefined as:

T _(distance) (voxel, d)=T ₀*(r−w·d)

where d is the distance from the voxel to the centre of mass of thetreatment volume, w is a weighting factor (i.e. for example 0<w<1), andT₀ can be any of the aforementioned transparencies T_(vulnerability),T_(importance) or T_(combined).

Returning to the example shown in FIG. 1, the first organ at risk OAR1exhibits a transparency T which is calculated in accordance with one ofthe above formulas to be for example 50%, hence rays emitted from thetreatment volume surface with an initial intensity value of I₀ areallowed to pass through this organ at risk OAR1 but their intensity isreduced by 50% when passing through the organ, irrespective of thedistance by which the respective ray passes through the organ. Inaccordance with an alternative approach, the transparency is set to be0.5 or 50% per unit length, thus causing the intensity to be reduced inaccordance with the following formula:

T _(ray exiting OAR) =I _(ray entering OAR)*(distance ray passes throughOAR)*0.5/unit length

Although not shown, it is possible for a single ray to pass through morethan one organ at risk, in which case the above formula is usedseparately and successively for each organ at risk and the respectiveindividual transparency is used (see for example Table 1 or 2), whereinthe value L_(ray exiting OAR) of a more interior organ at risk is usedas the value I_(ray entering OAR) for the next less interior organ atrisk, and so on.

An example calculation is performed, using for example hundreds of raystarting points on the treatment volume surface, wherein the raysstarting from a particular starting point are directed in all possibledirections or in a number of randomly selected directions. Since thetreatment volume (tumour) itself is considered to be opaque, the rays donot pass through this treatment volume and are only directed towards theoutside, i.e. towards the map surface.

As shown in FIG. 1, the treatment volume (tumour) has an exteriorright-hand starting point S1 which is located on the treatment volumesurface and an exterior left-hand starting point S2 which is likewiselocated on the treatment volume surface. Since the organ at risk OAR2 isconsidered to be an important organ and is thus assigned a transparencyT of 0%, no rays starting from the treatment volume can pass throughOAR2. Thus, the ray starting from the interior right-band starting pointS1 and touching the exterior right-hand point of OAR2 hits the mapsurface at the point M1, and the ray starting at the exterior left-handstarting point S2 of the treatment volume and touching the exteriorleft-hand point of OAR2 hits the map surface at point M2, such that themap surface between M1 and M2 cannot be reached by any ray emitted fromor starting from the treatment volume surface and following a straightline. Thus, the accumulated intensity is 0 and the intensity profile onthe map surface between M1 and M2 is shown in a deep black anddesignated as the “umbra”.

To the left of M2 in FIG. 1, the map surface can be reached by a numberof rays starting from the treatment volume surface. The greater thedistance from M2, the greater the amount of unattenuated rays whichreach the map surface, such that the accumulated intensity of a specificpoint on the map surface—being the sum of the intensities of all therays reaching this point—increases gradually with the distance of saidpoint from M2, until a point M3 on the map surface is reached. As shownin FIG. 1, points on the map surface further to the left of M3 and asfar as M5 are affected by the organ at risk OAR1, which attenuates someof the rays emitted from the treatment volume surface, such that theaccumulated or summed intensity of a respective map surface pointdecreases towards M6, as illustrated by areas which are more thicklyblackened than the area in the immediate vicinity of M3. From M6 to M5,the accumulated intensities increase again, as the attenuating effect ofOAR1 decreases.

To the right of M1 in FIG. 1, an ever increasing number of rays emittedfrom the treatment volume surface can reach the map surface, such thatthe summed intensities of the respective map surface points increase tothe right with the distance of the respective map surface point from M1.When the map surface point M4 is reached, which is the map surface pointat which all the rays emitted from the treatment volume surface canreach the map surface unattenuated, there is no reduction in intensityand this area on the map surface can thus be designated as “light”.

The same is true of the map surface area to the left of M5, where againall the rays emitted from the treatment volume surface can reach the mapsurface unattenuated, since neither OAR1 nor OAR2 attenuates orobstructs the emitted rays.

The areas between M1 and M4 on the right-hand side and between M2 and M5(thus including M3 and M6) on the left-hand side can be designated asthe “penumbra”.

Using the intensity profile on the map surface, it is possible todetermine that the best directions or angles to use for a radiationtreatment of the treatment volume will be those which project radiationinto the object and direct it to the centre of mass of the treatmentvolume or cause it to cover the entire extent of the treatment volume ortumour from the areas on the map surface identified in the intensityprofile as “light”, i.e. the areas to the right of M4 and to the left ofM5, since no organs at risk will be affected by such radiation. The nextmost expedient area would be the area around M3 on the map surface whichexhibits a summed intensity which is close to that of the “light” areas,although it is situated within the “penumbra” area, which means that atleast one of the organs at risk OAR may be slightly affected whenradiation is delivered to the treatment volume.

The “blacker” the respective area on the map surface is, the moresignificantly organs at risk will be affected and thus the less suitablethis area is for delivering radiation. If, for example, radiation isdirected to the treatment volume in the area between M1 and M2, theorgan at risk OAR2 will always be directly affected, which is however tobe avoided.

FIG. 2 shows a simple example embodiment of calculating an intensityprofile on a map surface, in which only the centre of mass of thetreatment volume, rather than the surface of the treatment volume, isconsidered to be the one source of light or rays. This leads to adiscrete intensity profile and possibly—as in the example shown, inwhich the organs at risk exhibit a transparency of 0%—to a digitalintensity profile which is less suitable for identifying expedient oroptimum points or directions for delivering radiation to the treatmentvolume.

FIG. 3 shows the example from. FIG. 1, but with the circle complete andrepresenting a cross-section of the map surface. As can be seen, if OAR1and OAR2 were the only two structures to be considered, the whole of thelower half of the map surface would exhibit the intensity profile“light”, since there are no organs at risk to obstruct or attenuate theintensity of the rays emitted from the treatment volume surface to themap surface.

An irradiation beam directed onto the treatment volume from the oppositehalf of the map surface (the lower half in FIG. 3) and starting betweenpoints M1′ and M2′ (which respectively represent the points M1 and M2 asmirrored at the centre of mass) will reach the treatment volume withoutaffecting any organ at risk. However, since the radiation will not stopat the treatment volume but rather exit the treatment volume, thisirradiation beam will inadvertently affect the organ at risk OAR2, whichis however to be protected from receiving any radiation.

In order to also take into account the effect of the rays exiting thetreatment volume, the intensity profile on the map surface can bemirrored at the centre of mass, which is for example the point ofsymmetry of the map surface, or can be calculated separately. In theexample shown, the penumbra and umbra intensity profile between M4 andM5 can be mirrored such that they are then also present on the oppositeside between M4′ and M5′. Thus, when considering the overall intensityprofile on the map surface, it will be clear that the best direction orarea for projecting radiation into the treatment volume is the “light”area between M4′ and M5 and between M4 and M5′, since the organs at riskOAR1 and OAR2 will not then be affected by any radiation at all, eitherbefore it enters the treatment volume or after it exits the treatmentvolume. If no such intensity profile which may be designated as “light”is available, the best area or direction for projecting radiation intothe treatment volume is that which exhibits the highest summedintensity, i.e. that which is closest to the designation “light” orwhich is the least black, which in the example shown in FIG. 3 would bethe area around M3 and the mirrored area M3′ which exhibits the same(for example mirrored) or a separately calculated intensity.

It would then be preferable to use M3′ as the starting point forirradiating the treatment volume rather than M3, because the slightlyvulnerable organs at risk would then only receive the radiation after ithad passed through and been attenuated by the treatment volume, whereasif M3 is taken as the starting point, a higher dose of radiation willreach the organ at risk first, before reaching the treatment volume.Accordingly, the intensity value at either M3 or M3′ should be modifiedto reflect this.

Thus, in a first step when mirroring the intensity profile at the centreof mass, the accumulated or summed intensity of one point, for exampleM3 (receiving for example 100 rays with an average intensity value of90, resulting in an accumulated or summed intensity of 100·90=9,000),and the summed intensity at the mirrored point, i.e. M3′ (receiving forexample 100 rays with an unattenuated intensity of 100, resulting in asummed intensity of 100·100=10,000), are compared.

Since it is preferable for an organ or structure which is to beprotected to be located behind the treatment volume, it is advantageousto add a predefined intensity value (of for example 1,000) to theintensity value of the point or mirrored point (i.e. M3 or M3′) whichexhibits the highest original intensity value. In the given example,this would be the intensity value of 10,000 at point M3′, which wouldthen be corrected to 11,000.

The respective intensities of the uncorrected mirrored points are thenadded to the intensities of the respective points. Thus, the intensityvalue at the point M3 would then be 19,000 (the original intensity of9,000 at M3 plus the original intensity of 10,000 at M3′).

The intensity at M3′ will thus be calculated to 20,000 (the originalintensity of 10,000 at M3′ plus the correction value of 1,000 plus theoriginal intensity of 9,000 at the mirrored point M3).

Once this calculation has been performed, it is easy to determine thatthe overall intensity of 20,000 at M3′ is higher than the overallintensity of 19,000 at M3, indicating that M3′ is a more expedientstarting point for irradiating the treatment volume than M3.

FIG. 4 schematically shows a radiation treatment device 1 which can bemoved in a circle around the patient's body 2 which includes a treatmentvolume and several organs at risk, such as those exemplified in FIGS. 1and 3. The radiation treatment device 1 emits a radiation or treatmentbeam 3 which is directed onto the treatment volume within the patient'sbody 2.

In accordance with the invention, switching the treatment beam 3 on andoff and positioning the treatment device 1 at any location along thecircular movement path 4 of the treatment device 1 is controlled by acontroller or PC which uses the method as described above. Once thepatient's body 2 has for example been registered using known methods,the treatment device 1 is moved to one or more positions between thepoints M4′ and M5 or between the points M4 and M5′ (the “light” areasfrom FIG. 3) and then switched on so as to emit a treatment beam 3 inorder to appropriately irradiate the treatment volume, while stillprotecting the organs at risk.

The intensity profile on the map surface, which corresponds to thecircular path 4 in FIG. 4, can also be displayed on a screen 5 which isconnected to the controller or PC.

The controller or PC which is able to perform the method in accordancewith the invention is also connected to a data source, such as an MRIscanner, in order to obtain raw data or pre-segmented data of thepatient's body or at least of a part of the object to be treated whichincludes the treatment volume.

1. A method for generating planning data or control data for a radiationtreatment, comprising the following steps: a) acquiring segmented dataof an object which contains a treatment volume and a non- treatmentvolume; b) modelling at least some or all of the volume or surface ofthe treatment volume as a source of light or rays exhibiting apredefined or constant initial intensity; c) modelling the non-treatmentvolume as comprising volumetric elements or voxels which each exhibit anindividually assigned feature or attenuation or transparency value(t_(min)≦t≦t_(max)) for the light or rays which feature is assigned tothe light or ray or which attenuation or transparency maintains orreduces the intensity of the light or ray as it passes through therespective volumetric element or voxel, wherein the feature orattenuation or transparency value is individually assigned to eachvolumetric element or voxel of the non-treatment volume; d) defining amap surface which surrounds the treatment volume or the object; e)calculating an accumulated intensity value for points or areas on themap surface, the accumulated intensity being the sum of the intensitiesof all the rays which exhibit the predefined or constant initialintensity and are emitted from the volume or surface of the treatmentvolume and reach a respective point on the map surface preferably byfollowing a straight line, wherein if the ray passes through anon-treatment volume or voxel, the intensity of the respective ray isreduced or attenuated by a factor which is determined by the individualfeature or attenuation or transparency value of the respectivenon-treatment volume or voxel; and f) generating an intensitydistribution on the map surface using the calculated accumulatedintensities.
 2. The method according to claim 1, wherein the generatedintensity distribution on the map surface is a function of theindividually assigned features and the individually assigned featurescan be varied after calculating the accumulated intensities to calculaterespective different intensity distributions on the map surface.
 3. Themethod according to claim 1, wherein the map surface is a sphere and thecentre of the sphere is located within the treatment volume or is thebarycentre of the treatment volume.
 4. The method according to claim 1,wherein the initial intensity of rays emerging from a part of thetreatment volume or its surface is increased, if the respective part ofthe treatment volume is determined to receive a higher dose ofirradiation during later radiation treatment.
 5. The method according toclaim 1, wherein the treatment volume is modelled to be fully opaque,such that no ray emitted from the surface of the treatment volume canpass through the treatment volume.
 6. The method according to claim 1,wherein the transparency value or opacity of each non-treatmentvolumetric element or voxel is determined on the basis of one or more ofthe following: the vulnerability of the volume or voxel to radiation;the importance of the volume or voxel; the distance from thenon-treatment volume or voxel to the treatment volume; and/or thedistance from the non-treatment volume or voxel to the outer contour orsurface of the object.
 7. The method according claim 1, wherein theaccumulated intensity on a map surface point is added to the accumulatedintensity value of one or each respective opposing map surface point,wherein the map surface point, the opposing map surface point and thebarycentre of the treatment volume are all situated on a straight line.8. The method according to claim 7, wherein an additional predefinedintensity value is added to the intensity value of the surface point oropposing surface point which exhibits the highest original accumulatedintensity value, before the accumulated intensity value of the opposingmap surface point is added.
 9. The method according to claim 1, whereinthe point on the map surface which exhibits the highest calculatedaccumulated intensity (I_(max)) of all the points is assigned a mapsurface intensity value of 100%, and map surface intensities between 0%and 100% (I_(i)/I_(max)) are calculated for the remaining point on themap surface, on the basis of this 100% map surface intensity value. 10.The method according to claim 9, wherein the areas or points on the mapsurface which exhibit the highest calculated accumulated intensity areused to define one or more suitable directions for irradiating theobject and/or are used to control the position and/or activation of aradiation device.
 11. The method according to claim 10, whereinradiation is only directed onto the object from points or areas whichexhibit a map surface intensity of 100% or more than 95%, 90%, 85% or80%.
 12. The method according to claim 11, wherein volumetric raycastingis used to generate a continuous intensity distribution on the mapsurface.
 13. A program which, when running on a computer or when loadedonto a computer, causes the computer to perform the method according toclaim
 1. 14. A program storage medium on which the program according toclaim 13 is stored, in particular in a non-transitory form.
 15. Acomputer on which the program according to claim 13 is running or intothe memory of which the program according to claim 13 is loaded.
 16. Aplanning or control system for a radiation treatment device comprising:the computer according to claim 15, for processing the three-dimensionalor volumetric image data of a body and for calculating a quantitativevalue indicating the suitability of possible radiation entry and exitpoints; a data interface for receiving the three-dimensional data andoptionally for outputting control data to an irradiation device; andoptionally a user interface for receiving data from the computer inorder to provide information to a user, wherein the received data aregenerated by the computer on the basis of the results of the processingperformed by the computer in accordance with the method accordingclaim
 1. 17. A radiation treatment device which is controlled withrespect to the position of the radiation-emitting element relative tothe body or treatment volume and/or with respect to the activation ofthe radiation-emitting element, on the basis of the intensitydistribution on the map surface generated in accordance with claim 1 oron the basis of the results of the data outputted from the computeraccording to claim 15 which quantitatively indicate which relativepositions or irradiation directions or points are preferred and/or lessharmful as compared to other possible irradiation points or directions.